1. Field of the Invention
The present invention relates to an apparatus for detecting anomaly of wheel speed sensors on the basis of at least rotational speeds of wheels (wheel speeds) detected by the wheel speed sensors.
2. Description of the Related Art
Conventionally, an apparatus for detecting anomaly of wheel speed sensors (hereinafter referred to as a “wheel-speed-sensor-anomaly detection apparatus”) has been known (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2000-344087). In general, such an apparatus utilizes a phenomenon that when a wheel speed sensor becomes anomalous, the wheel speed tends to be detected as a slower speed. That is, such an apparatus is configured such that when the wheel speed of a specific wheel, among the wheel speeds detected by wheel speed sensors disposed for individual wheels, is considerably lower than the wheel speeds of the remaining wheels, the wheel speed sensor of the specific wheel is determined to be anomalous.
Incidentally, when the gas pressure (typically, air pressure) of a tire decreases, the rolling resistance of the tire increases because of, for example, an increased area of the tire tread. As a result, when a vehicle is traveling on, in particular, a road surface having a low frication coefficient, such as an icy road surface, a wheel corresponding to a tire having a reduced gas pressure (hereinafter referred to as “gas-pressure-lowered wheel”) tends to lock, with the result that the actual wheel speed of the gas-pressure-lowered wheel may become lower than those of the remaining wheels.
In such a case, the above-described wheel-speed-sensor-anomaly detection apparatus raises a problem in that even when the wheel speed sensor of the gas-pressure-lowered wheel is normal, the apparatus erroneously determines that the wheel speed sensor of the gas-pressure-lowered wheel is anomalous.